1. Technical Field
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing an image on a recording medium and an image forming apparatus incorporating the fixing device.
2. Description of the Background
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include a fixing rotary body heated by a heater and an opposed body contacting the fixing rotary body to form a fixing nip therebetween through which a recording medium bearing a toner image is conveyed. As the fixing rotary body and the opposed body rotate and convey the recording medium bearing the toner image through the fixing nip, the fixing rotary body heated to a predetermined fixing temperature and the opposed body together heat and melt toner of the toner image, thus fixing the toner image on the recording medium.
Since the recording medium passing through the fixing nip draws heat from the fixing rotary body, a temperature sensor detects the temperature of the fixing rotary body to maintain the fixing rotary body at a desired temperature. Conversely, at each lateral end of the fixing rotary body in an axial direction thereof, the recording medium is not conveyed over the fixing rotary body and therefore does not draw heat from the fixing rotary body. Accordingly, after a plurality of recording media is conveyed through the fixing nip continuously, a non-conveyance span situated at each lateral end of the fixing rotary body may overheat.
To address this circumstance, the fixing device may incorporate a heat shield to shield the non-conveyance span of the fixing rotary body from the heater, thus preventing overheating of the fixing rotary body as disclosed by JP-2008-058833-A and JP-2008-139779-A, for example.
Additionally, if the heater accidentally generates an excessive amount of heat due to malfunction of the image forming apparatus, the heater may overheat the fixing rotary body. To address this circumstance, an abnormal temperature detector, such as a thermostat actuated as a safety device, may detect the temperature of the fixing rotary body. If the abnormal temperature detector detects the abnormal temperature of the fixing rotary body that is higher than a predetermined temperature, the heater is turned off.
However, the heat shield interposed between the heater and the fixing rotary body may create a shielded span on the fixing rotary body where the heat shield is interposed between the heater and the fixing rotary body to shield the fixing rotary body from the heater and an unshielded span on the fixing rotary body where the shield is not interposed between the heater and the fixing rotary body. The shielded span on the fixing rotary body may be heated slowly. Conversely, the unshielded span on the fixing rotary body may be heated quickly. Accordingly, if the abnormal temperature detector is configured to detect the temperature of the fixing rotary body at the shielded span thereof that is heated slowly, actuation of the safety device may be delayed.